Dosage-dispensing devices of this kind are used in particular for applications where small dosage quantities, for example of toxic substances, are dispensed with high precision into small receiving containers. In many cases such receiving containers are placed on a balance in order to weigh the substance that is discharged from the dosage-dispensing device, so that the substance can subsequently be processed further in accordance with given specifications.
A dosage-dispensing device which is described in EP 0 527 976 B1 has a housing with a receptacle for dosage material and a dispensing head which consists of an elastic material. The dispensing head, shaped like a baby bottle nipple, has a slit-shaped orifice which can be opened from the outside by applying a lateral force or pressure from two diametrically opposite directions. To prevent the formation of particle bridges during the dispensing of dosage material, such particle bridges can be broken up by a needle-shaped actuator.
The dosage-dispensing device disclosed in EP 0 527 976 B1 has the disadvantage that it is suitable only for dosage materials with good free-flow properties such as liquids, granulates, or special powders with particles that are approximately spherical and have a smooth surface. As soon as other kinds of powders are to be dispensed which are sticky or whose particles have a tendency to interlock with each other due to their shapes, even an actuator will be of little use. As described in EP 0 527 976 B1 as a solution for these cases, the housing of the dosage-dispensing unit can likewise be made of an elastic polymer material, which can be squeezed together from the sides like the slit-shaped orifice. As a result of the lateral compression the dosage material is pushed out of the receptacle compartment and expelled from the opened orifice. With this mode of discharge, an overpressure is produced inside the receptacle compartment, particularly if the latter is not completely filled with material, as the air in the receptacle compartment is being compressed. As soon as the outlet is opened, the compressed air pushes the dosage material through the outlet orifice. With very fine powdery dosage material this can have the consequence that the discharged particles are spread over a wide area instead of arriving in the receiving container. Besides the additional cleaning effort, this creates the danger in the case of toxic dosage material that the environment of the dosage dispensing device is being contaminated. Furthermore, with the material behaving in this way it can be difficult to achieve very precise deliveries of dosages in the milligram- or microgram range, as the loss rate due to the scattered material is largely random. Furthermore, the lateral compression of the housing can also have the effect that the dosage material is only being compacted instead of being delivered out of the dosage-dispensing device.
It is therefore the object of the present invention to create a dosage-dispensing device which has a dispensing head consisting of an elastic material and which allows the dosage material to be delivered in a precise and contamination-proof manner that is not affected by the flow properties of the dosage material.